Miyaoka

Prospect, Inactive

Alternative names

Miyaoka West

Commodities and mineralogy

Main commodities Cu; Zn
Other commodities As; Au
Ore minerals arsenopyrite; chalcopyrite; galena; pyrite; pyrrhotite; sphalerite

Geographic location

Quadrangle map, 1:250,000-scale MH
Quadrangle map, 1:63,360-scale C-6
Latitude 63.7127
Longitude -146.7414
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Miyaoka prospect is at an elevation of about 5,000 feet on the ridge east of the terminus of the east lobe of Hayes Glacier. The mineralized area is about 1,000 feet long and 200 feet wide. The center of the mineralization is about 0.3 mile southwest of elevation 5110 and about 0.6 mile west-southwest of the center of section 11, T. 14 S., R. 5 E.

Geologic setting

Geologic description

The rocks in the area are derived from Devonian felsic to intermediate volcanic rocks, mainly andesite, dacite, and quartz keratophyre flows and tuffs, and from Devonian or older shale, marl, and marble (Nokleberg and others, 1992 [MF]; 1992 [Open-File]). The rocks have been penetratively deformed, dismembered, and metamorphosed to chlorite-mica-quartz schist with marble and greenstone, first to lower-amphibolite-grade rocks in the Early Cretaceous and then retrograded to lower-greenschist-grade rocks in the mid-Cretaceous. Detailed mapping of the prospect by American Copper and Nickel Company in 1993 indicated that a felsic intrusion is infolded with mineralized schist and part of the mineralization may be a pyrrhotite-rich skarn (W.T. Ellis, unpublished data, 1993).
The Miyaoka prospect was discovered and sampled by the U.S. Geological Survey in the mid-1980s. American Copper and Nickel Company mapped and sampled the prospect in 1993 and it was examined and sampled by the Bureau of Land Management in the early 2000s.
The Miyaoka prospects consists of lenses, disseminations, and stringers of massive sulfides in the iron-stained metamorphic host rocks (Nokleberg and Aleinikoff 1985; Aleinikoff and Nokleberg, 1985; Nokleberg and others, 1991; Bittenbender and others, 1991). The massive sulfides are generally structureless but in places have a crude banding that parallels the layering in the metamorphic rocks. The sulfide minerals are predominantly pyrrhotite and pyrite with minor chalcopyrite; sphalerite, galena, and arsenopyrite are reported.
The mineralization occurs in two horizons that can be traced north-northwest for about 0.8 mile but the main zone of mineralization is about 1,000 feet long and 200 feet wide. Bittenbender and others (2007) collected 17 measured samples across the main zone of mineralization. The samples averaged 0.096 parts per million (ppm ) gold, 0.2 ppm silver, 784 ppm copper, 8.3 ppm lead, 54 ppm zinc, and 3.4 ppm arsenic. The highest-grade sample were: 27 feet that averaged 1.2 ppm gold; 6.2 feet that averaged 0.50 ppm silver; 4.9 feet that averaged 2,750 ppm copper; and 11 feet that averaged 14 ppm arsenic. A high-grade sample collected nearby had the highest metal content of the samples they collected: 7.1 ppm silver, 985 ppm lead, and 2,290 ppm zinc.
Geologic map unit (-146.743696169359, 63.7122811419512)
Mineral deposit model Kuroko massive sulfide (Cox and Singer, 1986; model 28a); related base-metal skarn.
Mineral deposit model number 28a
Age of mineralization Probably Devonian, the pre-metamorphic age of the host rocks.

Production and reserves

Workings or exploration The Miyaoka prospect was discovered and sampled by the U.S. Geological Survey in the mid-1980s. American Copper and Nickel Company mapped and sampled the prospect in 1993. Examined and sampled by the Bureau of Land Management in the early 2000s.
Indication of production None
Reserve estimates None.
Production notes None.

References

References

Bittenbender, P.E., Bean, K.W., Kurtak, J.M., and Deininger, James Jr., 2007, Mineral assessment of the Delta River Mining District area, east-central, Alaska: U.S. Bureau of Land Management, Alaska Technical Report 57, 675 p.
Lange, I. M., Nokleberg, W.J., Newkirk, S. R., Aleinikoff, J.N., Church, S.E., and Krouse, R.H., 1993, Devonian volcanogenic massive sulfide deposits and occurrences, southern Yukon-Tanana terrane, eastern Alaska Range, Alaska: Economic Geology, v. 88, p. 344-376.
Nokleberg, W.J., and Aleinikoff, J.N., 1985, Summary of stratigraphy, structure, and metamorphism of Devonian igneous-arc terranes, northeastern Mount Hayes quadrangle, eastern Alaska Range, IN Bartsch-Winkler, Susan, ed., The United States Geological Survey in Alaska--Accomplishments during 1984: U.S. Geological Survey Circular 967, p. 66-71.
Reporters W.T. Ellis (Alaska Earth Sciences), C.C. Hawley (Hawley Resource Group), and W.J. Nokleberg (USGS); D.J. Grybeck (Contractor, USGS)
Last report date 5/13/2012